Offline Files Synchronization Errors (Vista Sync Center)

This has got me stumped. My users' home folders are stored on a NetApp filer
(cifs). "My Documents" and "Favorites" are redirected and are made available
offline. On the filer, oplocks has been set to "on". When a user syncs his
offline files from his Windows Vista Enterprise computer, the "view sync
results" window displays a lot of errors (Details: "The process cannot access
the file because it is being used by another process."). On a Windows XP
computer, synchronization works like a charm.